It has been demonstrated that adult asthmatics have a decreased ventilatory response to hypoxia and hypercapnia, but it has not been shown whether asthmatic children also have a diminished response to these stimuli. The object of this research is to study Control of Respiration in asthmatic children by comparing their ventilatory responsiveness, respiratory drive, and pulmonary functions with that obtained from normal children. Ventilatory responsiveness is assessed by measuring ventilation during exposures to steady-state and progressive (rebreathing) isocapnic hypoxia and hyperoxic CO2. Indices of respiratory drive are obtained by measuring the pressure developed during the first 100 milliseconds of inspiration (P100) while the airway is occluded at the mouth and by measuring the work of breathing. P100 and work of breathing are determined with and without the addition of artificial inspiratory airway resistance during quiet breathing and while breathing is increased by excercise or through hypercapnic and hypoxic stimulation. Pulmonary functions are measured with a constant-volume body plethysmograph and with an automated spirometer.